Range-change transmissions having a multi-stage main transmission and a front-mounted group drive-coupled to the main transmission, upstream thereof, and having a range group drive-coupled to the main transmission, downstream thereof, have been known for some time and are preferably used in utility vehicles. Due to the front-mounted group usually having a two-stage design and a small transmission ratio increment, also called splitter group, the transmission ratio increment intervals between the transmission ratio stages of the main transmission are approximately halved, thus doubling the total number of available transmission ratio stages. By means of a typically two-stage range group, the gear range of the overall transmission is increased considerably and the total number of available gear ratio stages is again doubled. In combination with a three-stage main transmission (having three forward gears and one reverse gear), this results in a 12-gear range-change transmission (having a total of twelve forward gears and a maximum of four reverse gears) and in combination with a four-stage main transmission (having four forward gears and one reverse gear), in a 16-gear range-change transmission (having a total of sixteen forward gears and a maximum of four reverse gears).
Compared to a single transmission having a comparable number of gears and similar gear stepping and spreading, the range-change transmission is considerably more compact and lighter in weight. However, because multiple gear changes in a range-change transmission require changing transmission ratio stages in a plurality of sub-transmissions and are therefore relatively complicated, most known range-change transmissions are either semi-automatic or fully automatic in design.
An example of a method for operating a range-change transmission having at least one main group, one subgroup, and one central synchronization unit is known from DE 10 2010 009 673 A1. For reducing gear shifting times during a change of an overall transmission ratio, a subgroup shifting unit (for actuating the subgroup) and the central synchronization unit are actuated in parallel, at least intermittently. An actuation period of the central synchronization unit is settable using a (open- and closed-loop) control unit, wherein the actuation period is adjusted by means of an adaptation function.